What it looks like: http://puu.sh/hWIn

Excuse the poor-quality photo; I couldn't find any images or news posts about it anywhere. The King's speech bubble says "メンセージ", or "Message", and the background has animated stars flying towards the screen.

All Japanese 3DSes will receive the stationery automatically if they're Internet-connected. When you send out a message that uses this stationery, all of the recipients (as long as they've unlocked the Stationery function within Swapnote) will then be allowed to use it too; this is the only way to unlock it on 3DSes from other regions.

Therefore, if you want this for yourself, please leave your 3DS Friend Code in the comments and add mine:
0946-2283-6120
You should receive the stationery eventually.